The present invention is concerned with diagnostic test strips and a method for their optical identification.
Test strips for the analysis of components in a liquid such as a human body fluid are well known. Typically, such strips are made of an absorbent material in which there is absorbed a reagent system which responds to the presence of a pre-selected analyte in the test fluid with a visually detectable signal such as a change in color. This change in color, which appears in one or more test field of the strip, can be the result of an enzymatic reaction in which a redox dye is oxidized or reduced to produce the colored response. Alternatively, the strip is made of a material through which the analyte and labeled antibodies specific therefor can flow to form analyte/labeled antibody conjugates which are captured in a specific detection zone of the strip to provide a detectable response when analyte is present in the fluid sample. These devices can employ either a sandwich type format in which the response is directly proportional to the concentration of the analyte in the test fluid or a competitive format where the intensity of the response is inversely proportional to the analyte concentration. While the detectable response obtained using such strips can be observed visually to obtain a qualitative or semiquantitative measure of the analyte in the test sample, greater quantitation and faster, more reliable handling of multiple test strips can be realized by reading the developed test strips instrumentally, typically by the use of a reflectance spectrometer which determines the intensity of reflection from the test field surface. This sort of instrument determines the intensity of the reflected light in the developed strip by illuminating the strip with light at one angle (typically 90.degree.), detecting the reflected light at a different angle (typically 45.degree.) and selecting the measured color or wavelength range at either the source or detector. The signal at the detector is typically amplified, converted to digital form and analyzed by computer. Conventionally, at the beginning of the test, the operator of the device will input information via a keyboard or other means to tell the instrument what analyte the particular strip is designed to test, so that the read out may be correlated with an appropriate reference. Thus, if the test were designed to determine the presence of hCG in the test sample, the read out would be correlated with a reference value corresponding to the presence of hCG. Because of the need for operator input, the degree of automation of the operation is less than complete and various techniques have been developed to further automate the process by providing the strips with indicators from which the device can determine the analyte to which a particular test strip is directed without the need for operator intervention.
An example of such an automated system is described in U.S. Pat. No. 5,439,826. This disclosure involves a microstrip containing a series of wells for ELISA assays in which the individual wells contain a physical characteristic, such as reflectance, in a predetermined order. The instrument detects the presence or absence of the physical characteristic and interprets this as a binary response which correlates with the particular analyte.
In U.S. Pat. No. 4,592,893 there is disclosed an analysis test strip having a test field and a separate bar code for storing batch specific information necessary for the quantitative evaluation of the reaction carried out on the test field. The bar code consists of individual code bars of differing width running substantially transversely to the longitudinal dimension of the test strip. The code bars are of narrow and broad width and the batch specific information is designed to be interpreted by a reading device in which a narrow bar represents a logical 0 and a wide bar represents a logical 1 with the distances between the code bars providing similar information. The strip reading device is programmed to interpret the logical 0 and 1 responses as a binary code corresponding to the batch specific information imputted to the test strip.
U.S. Pat. No. 5,126,952 discloses a method of providing data in bar code form useful for the determination of the calibration curve of a lot of test elements in a chemical analyzer wherein the curve corresponds to the mathematical formula: EQU C=a.sub.0 -a.sub.1 .multidot.R-a.sub.2 .multidot.(R).sup.K
where C is the predicted concentration of the fluid test sample being analyzed, R is the response actually measured in the analyzer, K is a coefficient assigned to the analyzer and a.sub.0, a.sub.1 and a.sub.2 are calibration coefficients. It is stated that solving this equation as described in the patent is advantageous in that a single bar code strip of only a few digits can be accurately provided with the data needed to pass on a calibration code for a given lot of test elements to the user.